High frequency and high sensitivity ultrasound imaging at the frequency range of 30-100MHz is capable of resolving structures almost down to the cellular level. Developing such an imaging modality for clinical use could have a tremendous impact on the diagnostic and therapeutic procedures in many different clinical areas. The cardio-vascular clinician will be able to visualize in great detail the arterial walls of the coronary arteries and the heart interior structure. The diagnostics of cancer using biopsy will be revolutionized as in-situ microscopy could replace the traditional procedure. Imaging guided therapy could be developed since the diagnosed pathology can be localized at a great precision. The technology can enable high resolution intravascular ultrasound (IVUS) imaging and early cancer detection. In this R01 program, we propose to develop novel optical techniques for high-frequency and high-sensitivity ultrasound detection and broadband ultrasound generation. The proposed work is built upon our initial results obtained through a previous exploratory R21 program and some very recent experimental work related to certain proposal aims. To develop this novel imaging technology many technical and scientific problems must be addressed. It is the aim of the work proposed here to investigate the following tasks in detail with an emphasis on the understanding of underlying physical principles and explore a number of candidate device structures to lay down a solid foundation for the future implementation of integrated transducer arrays for intravascular and intra-catheter applications. The specific aims are: 1. Develop high-frequency and high-sensitivity ultrasound receivers by using microring resonators with very high quality factor resonances, characterize their sensitivity and dynamic range. 2. Develop high-resolution ultrasound receivers using compact microring and microdisk resonator platforms 3. Design integrated optics elements acting as ultrasound generators using photoelastic methods. The LSPR effect of metallic nanoparticles will be exploited [and embedded in polymer waveguide] for efficient conversion of laser power to broadband acoustic signal. 4. Integrate a prototype imaging device. The prototype will consist of at least 8 microring elements forming the receiver array and one or distributed photoacoustic transmitters. Such an imaging device will be tested for potential catheter-based application as a "smart needle" for high resolution imaging of kidney and diagnosing renal diseases.